This invention relates to a method of producing a copper-based material for a plain bearing, and more particularly to a method of producing a sintered bimetal for use as a material for a plain bearing which bimetal has a layer of copper-lead alloy, a lead-bronze alloy, or a bronze alloy, bonded to a back metal.
The present invention is intended to improve conventional methods of producing a bearing material, and is directed to a method of producing a bimetal for a copper based alloy plain bearing for use in various equipment and machines required to achieve low cost and high performance, such as an automobile, ship, electric equipment, office automation equipment, agricultural machines, machine tools, food machines, and other industrial machines.
In a conventional method of producing a copper-based bearing material, copper alloy powder is spreaded onto a back metal, and then the back metal with the powder is introduced into an electric furnace or a gas furnace where the powder is subjected to a primary sintering in a reducing atmosphere, and then a porous alloy layer resulting from the above sintered powder is compressed by a primary rolling, and then this intermediate product is again introduced into an electric furnace where the alloy layer is subjected to a secondary sintering so as to enhance the degree of sintering of the alloy layer, and then a secondary rolling is carried out to effect the sizing and to increase the strengths of the alloy layer and the back metal.
In such a method of producing a copper-based sintered bimetal, the best way of reducing the cost is to increase the sintering speed. However, with the conventional resistance-heating method performed by a heating element of the electric furnace, the material is heated by radiation heat from the heating element, bricks, or a muffle, and therefore it takes considerable time to heat the material to the sintering temperature, thus failing to achieve an increased sintering speed. Therefore, in order to increase the sintering speed, the length of the electric furnace has been increased, or the sintering temperature has been increased. However, a space available in a plant or factory is limited. And besides, when the temperature is increased, the sintering is liable to be excessive, so that the quality of the product is not stable. Thus, it is difficult to achieve a satisfactory control during the production at the plant. Further, where the thick back metal is used, it takes much time to heat the back metal, and the surface of the alloy is heated faster than the inner part of the alloy and the bonding part As a result, the sintering starts from the surface of the alloy, so that the thus sintered surface prevents a reducing gas from flowing toward the inner part of the ally, thus failing to obtain a satisfactory bonding strength and a satisfactory strength of the alloy. In view of this, a preheat zone is provided at the sintering furnace, and the powder and the back metal are heated to a temperature slightly lower than the temperature of sintering of the alloy to thereby effect in a reducing atmosphere the reducing of both the powder and the bonding surface of the back metal, and thereafter the sintering is carried out in a main sintering zone. Therefore, this method suffers from the problem that the sintering speed is decreased or the problem that the length of the furnace is made longer.